1. Field of the Invention
The present general inventive concept relates to a developing unit in which a developer cartridge is detachably mounted, and an image forming apparatus having the developing unit.
2. Description of the Related Art
FIGS. 1 and 2 are views illustrating an example of an image forming apparatus.
In FIG. 1, the image forming apparatus capable of color printing includes a feeding unit 10, a plurality of developing units 20, a transferring unit 30, a fixing unit 40 and a discharging unit 50.
An image is printed on a sheet of paper picked up by the feeding unit 10 while the sheet of paper passes through the developing unit 20 and transferring unit 30. The printed image is then fused by the fixing unit 40, and the fused image is discharged to the outside of the image forming apparatus.
FIG. 2 is an enlarged view of the developing units 20 of FIG. 1. In FIG. 2, each of the developing units 20, which have different color toners, includes a developing roller 21, a photosensitive medium 22 and a cleaning unit 23, which are integrated with their respective developing units 20. A developer contained in the developing units 20 may form clumps over time due to internal stress, and accordingly vertical streaks may appear on the image during printing. In order to eliminate such streaks, the developer must be thoroughly agitated, and then supplied to the developing roller 21.
The developing roller 21, photosensitive medium 22 and cleaning unit 23 integrated with their respective developing units 20 of a compact image forming apparatus are often made to have similar service lives. However, in the case of a large-scale image forming apparatus (e.g., one used in an office), numerous sheets of paper are printed and the developer becomes exhausted more rapidly than the photosensitive medium 22 and cleaning unit 23. In order to reduce maintenance costs incurred by a user, a developer cartridge is needed which can supplement the developer without having to also replace the entire developing unit.
Accordingly, if a detachable developer cartridge is provided, the user can reduce maintenance costs for consumables, but various problems can arise when the developer contained in the developer cartridge is supplied to the developing unit.
For example, a separate supplying unit may be required to supply the developer discharged from the developer cartridge to the developing unit, which causes additional inconvenience for the user. Since the developer discharged from the developer cartridge tends to stick together, an image may not be uniformly printed if the developer is not sufficiently agitated. Thus, a structure which enables the supplied developer to be agitated may also be required according to the configuration of the supplying unit.